Kineticomechanistic Study of the Redox pH Cycling Processes Occurring on a Robust Water-Soluble Cyanido-Bridged Mixed-Valence {CoIII/FeII}2 Square.

A kineticomechanistic study of reversible electron-transfer processes undergone by the water-soluble, cyanido-bridged mixed-valence [{CoIII{(Me)2(µ-ET)cyclen}}2{(µ-NC)2FeII(CN)4}2]2- square has been carried out. The oxidation reaction consists of a two-step process with the participation of a solvent-assisted outer-sphere complex, as a result of the establishment of hydrogen bonds that involve the oxo groups of the oxidant (peroxodisulfate) and the terminal cyanido ligands of the tetrametallic square. The formally endergonic reduction reaction of the fully oxidized ([{CoIII{(Me)2(µ-ET)cyclen}}2{(µ-NC)2FeIII(CN)4}2]) core by water, producing hydrogen peroxide from water even at low pH values, is also a two-step process. Each one of these processes requires a set of two preequilibria involving the association of OH- and its subsequent deprotonation by a further OH- anion. The structure of the square compound in its fully protonated form has also been determined by X-ray diffraction and shows the existence of strong hydrogen-bonding interactions, in agreement with the rather high basicity of the terminal cyanido ligands. Likewise, density functional theory calculations on the tetrametallic complex showed zones with negative electrostatic potential around the FeII centers of the square that would account for the establishment of the hydrogen bonds found in the solid state. Spectroelectrochemistry experiments demonstrated the singular stability of the {CoIII/FeII}22- complex, as well as that of their partially, {Co2III/FeIIIFeII}-, and fully, {CoIII/FeIII}2, oxidized counterparts because no hysteresis was observed in these measurements.

Redox-Assisted Self-Assembly of a Water-Soluble Cyanido-Bridged Mixed Valence {CoIII /FeII }2 Square.

The facile redox-assisted assembly of a water-soluble, extremely robust, cyanide-bridged mixed-valence [{CoIII {(Me)2 (µ-ET)cyclen}}2 {(µ-NC)2 FeII (CN)4 }2 ]2- square is reported. The preparation process involved the use of the enhanced lability of inert CoIII synthons triggered by outer-sphere redox processes. Characterization of the final compounds has been carried out by NMR, UV/Vis, electrochemistry, and ICP analyses. DFT calculations have been conducted to optimize a structure that has the same hydrodynamic radius as that obtained from DOSY experiments. The new compound is extremely robust, surviving in aqueous solution within the 0-12 pH range for months. The species shows a high affinity for both protons and hydroxo ions in aqueous medium.

Manganese clusters derived from 2-pyridylcyanoxime: new topologies and a large spin ground state in pyridyloximate chemistry.

Series of manganese clusters derived from 2-pyridylcyanoxime with Mn3(II) (1), Mn4(II) (2a, b), Mn(II)4Mn(III)4 (3), Mn(II)2Mn(III)6Mn(IV)2 (4) and Mn(II)3Mn(III)6Mn(IV) (5) cores have been characterized. Dc magnetic measurements reveal antiferromagnetic coupling for 1-4 and dominant ferromagnetic interactions for 5 which shows the largest ground state reported to date in pyridyloximate chemistry (S = 14).

High nuclearity in azido/oximate chemistry: Ni14 and Ni13 clusters with S = 6 and 9 ground states.

In the present work, we report a family of Ni(14) and unprecedented Ni(13) clusters linked by end-on azido and oximato bridges. Ferrimagnetic response gives S = 6 and 9 ground states, resulting in the largest nuclearities and spins in nickel oximato chemistry.